Input devices (e.g., a touch screen or touch pad) are designed to detect the application of an object and to determine one or more specific characteristics of or relating to the object as relating to the input device, such as the location of the object as acting on the input device, the magnitude of force applied by the object to the input device, etc. Examples of some of the different applications in which input devices may be found include computer display devices, kiosks, games, automatic teller machines, point of sale terminals, vending machines, medical devices, keypads, keyboards, and others.
Currently, there are a variety of different types of input devices available on the market. Some examples include resistive-based input devices, capacitance-based input devices, surface acoustic wave-based devices, force-based input devices, infrared-based devices, and others. While providing some useful functional aspects, each of these prior related types of input devices suffer in one or more areas.
Resistive-based input devices typically comprise two conductive plates that are required to be pressed together until contact is made between them. Resistive sensors only allow transmission of about 75% of the light from the input pad, thereby preventing their application in detailed graphic applications.
Capacitance-based input devices operate by measuring the capacitance of the object applying the force to ground, or by measuring the alteration of the transcapacitance between different sensors. Although inexpensive to manufacture, capacitance-based sensors typically are only capable of detecting large objects as these provide a sufficient capacitance to ground ratio. In other words, capacitance-based sensors typically are only capable of registering or detecting application of an object having suitable conductive properties, thereby eliminating a wide variety of potential useful applications, such as the ability to detect styli and other similar touch or force application objects. In addition, capacitance-based sensors allow transmission of about 90% of input pad light.
Surface acoustic wave-based input devices operate by emitting sound along the surface of the input pad and measuring the interaction of the application of the object with the sound. In addition, surface acoustic wave-based input devices allow transmission of 100% of input pad light, and don't require the applied object to comprise conductive properties. However, surface acoustic wave-based input devices are incapable of registering or detecting the application of hard and small objects, such as pen tips, and they are usually the most expensive of all the types of input devices. In addition, their accuracy and functionality is affected by surface contamination, such as water droplets.
Force-based input devices are configured to measure the location and magnitude of the forces applied to and transmitted by the input pad. Force-based input devices provide some advantages over the other types of input devices. For instance, they are typically very rugged and durable, meaning they are not easily damaged from drops or impact collisions. Indeed, the input pad (e.g., touch screen) can be a thick piece of transparent material, resistant to breakage, scratching and so forth. There are no interposed layers in the input pad that absorb, diffuse or reflect light, thus 100% of available input pad light can be transmitted. They are typically impervious to the accumulation of dirt, dust, oil, moisture or other foreign debris on the input pad. Force-based input devices comprise one or more force sensors that are configured to measure the applied force. The force sensors can be operated with gloved fingers, bare fingers, styli, pens pencils or any object that can apply a force to the input pad. Despite their advantages, force-based input devices are typically too large and bulky to be used effectively in many touch screen applications. Additionally, conventional force-based input devices, as well as most other types of input devices, are capable of registering touch from only one direction, or in other words, on one side of the input pad, thereby limiting the force-based input device to monitor or screen-type applications.
Infrared-based devices are operated by infrared radiation emitted about the surface of the input pad of the device. However, these are sensitive to debris, such as dirt, that affect their accuracy.